Current-collecting device



May 27 1924.

O. H. ESCHHOLZ ET AL.

CURRENT COLLECTING DEVICE Filed April 16 1923' INVENTORS OH-o H Eschholz,@ ErrBoYl B. Sharwd.

WITNESSES ATTORN EY Patented May 27, 1924.

UNITED STATES PATENT OFFICE.

OTTO H. ESCHHOL Z, OI WILKINSBURG, AND ERBOL B. SKAND, OI" PITT SBURGH, PENN- SYLVANIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC & MANUFACTURING COM- PANY, A CORPORATION OF PENNSYLVANIA.

' manner-commune nnvxcn.

Application filed April 10, ms. Serial no. aaaiai.

To all whom it may concern:

Be it known that we, Om H. ESCHHOLZ,

a citizen of the United States, and a resident of Wilkinsburg, in the county of Alleheny and State of Pennsylvania. and

RROL B. S-HAND, a subject of the King of Great Britain, and a resident of Pittsburgh,

in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Current-Collecting Devices, of which the following is a specification.

Our invention relates, in general, to ourrent-collectin devices, -and it has for its 1 particular ob]ect to secure improvements in the electrical and mechanical operation of brushes, collecting currents from slip-rings.

In the operation of dynamo-electric machines, where large currents are conveyed from stationary to movable parts, as in rotary converters, for example, the electrical wear of brushes has been found to impose a serious limitation upon the performance of the machines.

As a result of an extensive investigation, we have found that one of the principal sources of rapid brush wear lies in unequal current distribution between brush contact and collecting surfaces that is caused chiefly by a wedge-shaped air-film between the brush and collector ring, as will be more fully explained hereinafter.

The principal object of our invention is, therefore, to provide means for, and methods of, either preventing the formation of such films or counteracting the harmful effects thereof.

With the above and other objects in view, our invention consists in the methods and structural details hereinafter described and claimed, and illustrated in the accompanyin drawings wherein,

igure 1 is a side view in elevation of a part of a slip-ring embodying our invention;

Fig. 2 is a top plan view of a portion of the slip-ring shown in Fig. 1;

Fig. 3 is a view similar to Fig. 2, showing a modified form of our invention;

ig. 4 is an elevational view of a slip-ring embodying another form of our invention;

Fig. 5 is a side view of a brush embodymg our invention and co-operating witha smooth collector ring;

Fig. 6 is an elevational view of another by .an arrow 3. The spaces between the slots are preferably such that a brush 4 co-operating with the ring always has a plurality of slots thereunder. For example, we have obtained remarkably good results with slots wide and *3 apart and brushes 1%" wide in the circumferential direction.

Our invention isv founded upon the knowledge that, with a smooth collector ring of the usual type, operating with an ordinary brush, a film of air adheres to the surface of the rotating collector ring and is dragged under the brush, the viscosity of the air at ordinary slip-ring speeds being suflicient to produce a wedge-shaped air cushion under the brush. By drilling test holes through the toe and the heel of a brush, we have experimentally demonstrated the fact that there is an air pressure, approximating 1 pound per square inch, under the toe of the brush, whereas the air pressure under the heel is much smaller and may even be suction. Oscillographic observations have also disclosed a definite tendency to pass less current at the toe than at the heel of the brush.

In Fig. 7, dotted-line curves 7 and 8, respectively show the airressure, for different; slip-ring speeds un er the toe and the heel of a brush operating on a smooth collector ring, while full line curves 9 and 10, respectively, show the air pressure under the toe and the heel of the same brush operatingwith a ring which is slotted as hereinbefore described. As will be seen from the curves, the effect of slotting is very pronounced in-securing an equilization of the ressure under the brush and preventing the ormation of the wedge-shaped air-film.

The air pressures as in dicated in Fig. 7 are subject to wide variations from time to time, depending upon minor changes in the operating conditions of the brush; and where several brushes are operating in parallel there will, in general, exist a cons derable difference in the pressure maintained under the individual brushes, resulting 1n unequal contact drop and unbalanced current distribution between the brushes. The reduction of the air-film reduces greatly the pressure fluctuations and contributes directly to a more uniform current distribution be tween brushes operating in parallel.

In considering the wear of the brushes, we have to distinguish between themechanical wear resulting from the abrasive action of the revolving collector ring and the electrical wear resulting from heating and burning of the brush caused by the electrical current.

It might be thought that the above-described method of improving the electr cal wear of the brushes is impractical as bemg open to the objection of increasing the mechanical wear. Numerous brush tests were made, therefore, with brushes running idle, or without current, on slotted rings and unslotted rings. It was found that the 1ncreased wear due to slottin was so small, as to be a negli ible factor 1n the combined mechanical an electrical wear of the brushes.

A11 investigation was also made to ascertain the combined electrical and mechanical wear of brushes bearing on sli -rings with and without slots, and it was ound that a very considerable saving in the total brush wear is obtained by the use of slots. The brush wear, in inches per hundred hours run, is plotted in Fig. 8 as a function of the current density in am eres per square inch of the brush surface,- or two types of sliprings. Curve 11 was obtained when using a smooth slip-ring and curve 12 when using a slip-ring slotted in accordance with our invention. The collector rings were operated at a speed of 4700 feet per minute.

The limitations imposed by the wedgeshaped air space beneath the brush may be overcome in other ways than by slotting the rings. Thus, Fig. 3 shows a collector ring having small holes or depressions 13 providing spaced air pockets in suflicient numbers to relieve the excessive pressure and secure good contact at the toe of the brush.

In Fig. 4 is shown another modification in which a collector ring is provided with perforations 14 extending through the full depth of the ring. The perforations may be spaced in a way similar to the holes 13 in Fig. 3, and are shaped so that with the slipring rotating in the direction indicated by the arrow 3 suction is created under the brush. The sucking action just described contributes to the maintenance of. uniform pressure conditions upon the bearing surface of the brush.

In Fig. 5 is shown an embodiment of our invention wherein channels 15, extending radially in the leading side of a brush 4, serve to relieve the excessive pressure under the brush toe.

In Fig. 6 is shown an embodiment of our invention combining a channeled brush 4 and a ring 1 having axial slots 2 and perforations 14 through the depth of the ring and arranged to create suction under the brush surface.

While We have described a few practical embodiments of our invention; other modifications thereof will be evident to those skilled in the art, and it is our desire that the accompanying claims shall be construed to cover any equivalents comprehended by the lan age thereof.

We 0 aim as our invention l. A current-collecting device comprising a rotating slip-ring and a brush member cooperating therewith, said slip-ring being provided with air-vent passages to prevent the uneven distribution of air pressure between the contact surfaces of the brush member and slip-ring.

2. A current-collecting device comprising a slip-ring and a brush member co-operating therewith, said slip-ring being provided with a plurality of depressed air-vent passages in the surface thereof with which the brush member contacts to equalize the air-film pressure between the contact surfaces of the slip-ring and brush member.

3. A current-collecting device com rising a rotating slip-ring and a brush mem er cooperating therewith, said slip-ring being provided with a plurality of depressed airvent passages disposed in the surface thereof with which the brush member contacts, transversely of the direction of rotation and extending thereacross, to counteract the formation of air film between the contact surfaces of the brush member and slip-ring.

4. A current-collecting device, comprising a rotating slip-ring and a brush member cooperating therewith, said slip-ring being provided with a pluralit of air-vent passages, disposed in the b0 y portion, extending radially from the contact surface thereof and opening to the atmosphere at their opposite ends, said passages being so spaced that the brush member, during operation, always has at least one air passage under the leading half of the brush contact surface.

5. A current-collecting device com rising a rotating slip-ring and a brush mem er cooperating therewith, each of said members being provided with a plurality of co-operating air-vent passages disposed within their body portion and extending therethrough' from the contact surfaces of said members, terminatin with both extremities open to the atmosp ere to counteract the formation of an air film between the contact surface of the brush member and the slip-ring.

6. A current-collecting device comprising a slip-ring and a brush member co-operating therewith, said members being provided with air-vent passages inter-communicating with each other and with the leadin side of the contacting surfaces of the sip-ring and brush member to create a suction in said air vent passages and between the contact surfaces at their leading side.

7 A current-collecting device comprising a slip-ring and a brush member co-operatin therewith, said slip-ring being provide upon its surface, with a plurality of depressions, the spacing between said depression's being such that said brush member always has, during operation, at least one such depression under its leading side.

8. A current-collecting device comprising a slip-ring and a brush member co-operating therewith, said slip-ring having, in its contact surface, a plurality of channels having an axial extent greater than the axial width of the brush and spaced circumferentially in such distances that a plurality of channels are always spanned by the brush.

In testimony whereof, we have hereunto sggscribed our names this 12th day of April, 1 3.

OTTO H. ESCHHOLZ. ERROL B. SHAND. 

